Method for manufacturing a MOS transistor that prevents contact spiking and semiconductor device employing a MOS transistor made using the same

ABSTRACT

A method for manufacturing a metal-oxide-semiconductor transistor prevents the occurrence of a contact spiking phenomenon. The method includes forming a metal thin film and an isolation oxidation film on a semiconductor substrate, and selectively etching the isolation oxidation film such that the isolation oxidation film is left remaining only over a field oxidation film; heat treating the semiconductor substrate to form silicide by the metal thin film in gate, source, and drain regions; removing portions of the metal thin film that is not formed into silicide, that is, removing unreacted metal thin film; removing the isolation oxidation film left remaining on the field oxidation film; and heat treating the semiconductor substrate in an oxygen environment to form the unreacted metal thin film remaining on the field oxidation film into a metal oxidation film. The present invention is related also to a semiconductor device that employs a metal-oxide-semiconductor transistor made using the method.

BACKGROUND OF THE INVENTION

(a) Field of the Invention

The present invention relates to a method for manufacturing a MOS(metal-oxide-semiconductor) transistor of a semiconductor device. Moreparticularly, the present invention relates to a method formanufacturing a MOS transistor that prevents contact spiking (i.e.,excessive etching) of a field oxidation film adjacent to a device regionduring etching to form contact holes. The present invention relates alsoto a semiconductor device employing a MOS transistor manufactured usingthe method of the present invention.

(b) Description of the Related Art

There are two general classes of field effect transistors (FETs) andthey include the MOSFET and the JFET (junction FET). The presentinvention is related to the MOSFET. The MOSFET typically includes on asemiconductor substrate the electrodes of a source, a drain, and a gate.Metal interconnect lines are connected to upper areas of the source,drain, and gate to allow application of electrical signals to the same,and the electrodes and the metal interconnect lines are electricallyconnected through contact formed at contact hole.

In order to minimize the resistance of each of the electrodes, silicidefilms are formed between the metal interconnect lines and each electrodeof the source, drain, and gate. A silicon nitride film, which functionsas an etching completion layer during etching to form contact holes, isdeposited over an entire upper surface of the transistor that includesthe silicide films.

FIGS. 1A to 1B are partial sectional views used to describe aconventional method for manufacturing a MOS transistor.

With reference to FIG. 1A, thermal oxidation of a silicon wafer 1, onwhich a device region is defined, is performed by a field oxidation film2 using a LOCOS (local oxidation of silicon) or trench process such thata gate oxidation film 3 is grown on a surface of the device region ofthe silicon wafer 1. After depositing polysilicon, which will be usedfor gate electrodes 4, over an entire upper surface of the silicon wafer1, the polysilicon and the gate oxidation layer 3, are patterned to apredetermined width.

Next, a p-type or n-type dopant is ion-injected at a low concentrationon the device region of the silicon wafer 1 using a mask. As a result,LDDs (lightly doped drains) 5 are formed on the device region of thesilicon wafer 1, as are side walls 6 to both sides of the gate oxidationfilm 3 and the gate electrode 4. Following this operation, a conductingdopant identical to that used for the LDDs 5 is ion-injected at a highconcentration on the device region of the silicon wafer 1 using a maskto thereby form a source 7 and a drain 7.

Subsequently, titanium is deposited to a thickness of approximately 400Å over the entire surface of the silicon wafer by a sputtering method,then RTP (rapid thermal processing) is performed for about 30 secondsand at a temperature of roughly 750 Å while injecting nitrogen at a flowrate of approximately 50 sccm. As a result, with reference to FIG. 1A,titanium silicide 8′ is formed by the reaction between titanium andsilicon. The titanium on the side walls 6 and the field oxidation film 2is not reacted and therefore remains as unreacted titanium.

The unreacted titanium is a metal and so may interfere with deviceoperation. The unreacted titanium is therefore removed using a solvent.Also, in order to reduce the resistance of the silicide 8′ and increasethe strength of the same, a heat process is performed in a nitrogenenvironment and at a temperature of approximately 910 Å.

After the above processes, in order to form a liner film that is used asan etching completion layer during etching to form contact holes, asilicon nitride film 9, with reference to FIG. 1A, is formed to athickness of roughly 300 Å using plasma enhanced chemical vapordeposition (PECVD).

In the above process, the silicon nitride film 9 is less thicklydeposited at depressed areas adjacent to the device region (one of whichis circled using a dotted line in FIG. 1A) than in other areas. Thedepressed areas are formed as a result of structural problems occurringwhen forming the field oxidation film 2.

Next, an insulating layer, that is, a pre-metal dielectric (PMD) layer10 is thickly formed by using atmospheric pressure chemical vapordeposition (APCVD) on the silicon nitride film 9, after which the PMDlayer 10 is heat treated to improve the strength of the same. Chemicalmechanical polishing (CMP) is then performed to flatten the PMD layer10.

Subsequently, to prepare for the formation of contact holes, aphotosensitive film pattern 11 is formed on the flattened PMD layer 10.With reference to FIG. 1B, exposed areas of the PMD layer 10 are thenetched using the photosensitive film pattern 11 as a mask to therebyform contact holes 12.

Next, TiN 13 is then thinly deposited as a barrier metal film over theentire upper surface of the silicon wafer 1, after which tungsten 14 isused to fill the contact holes 12.

In the above conventional method for manufacturing a MOS transistor, thesilicon nitride film 9, which is used as an etching completion layer, isnot formed to a uniform thickness. As a result, when etching the PMDlayer 10, the areas of the silicon nitride film 9 formed over thedepressed areas of the field oxidation film 2 adjacent to the deviceregion are more quickly etched than other areas of the silicon nitridefilm 9. Therefore, a contact spiking phenomenon occurs, in which thesilicon nitride film 9 is over-etched past where the field oxidationfilm 2 (under these areas of the silicon nitride film 9) starts. Onesuch area is circled using a dotted line in FIG. 1B. The contact spikingphenomenon ultimately results in the interference of the flow of currentin the source 7 and the drain 7 such that the semiconductor deviceoperates improperly.

Such a contact spiking phenomenon may also occur as a result ofmis-alignment of the photosensitive film pattern 11 when forming thesame to form the contact holes 12.

SUMMARY OF THE INVENTION

It is an advantage of the present invention to provide a method formanufacturing a MOS (metal-oxide-semiconductor) transistor of asemiconductor device that prevents the occurrence of the contact spikingphenomenon in which a field oxidation film is excessively etched duringetching of an insulating layer in order to form contact holes.

It is another advantage of the present invention to provide asemiconductor device employing a MOS transistor manufactured using themethod of the present invention.

In the present invention, part of an unreacted metal thin film that isunused when forming silicide is left remaining over a field oxidationfilm such that excessive etching of the same is prevented.

In one embodiment, the present invention includes a method formanufacturing a metal-oxide-semiconductor transistor. The methodincludes forming a metal thin film and an isolation oxidation film on asemiconductor substrate, and selectively etching the isolation oxidationfilm such that the isolation oxidation film is left remaining only overa field oxidation film; heat treating the semiconductor substrate toform silicide by the metal thin film in gate, source, and drain regions;removing portions of the metal thin film that is not formed intosilicide, that is, removing unreacted metal thin film; removing theisolation oxidation film left remaining on the field oxidation film; andheat treating the semiconductor substrate in an oxygen environment toform the unreacted metal thin film remaining on the field oxidation filminto a metal oxidation film.

Preferably, the isolation oxidation film is formed by performingdeposition to a thickness of 300˜500 Å using plasma enhanced chemicalvapor deposition, and the metal oxidation film is formed by performingrapid thermal processing in an oxygen environment, at a temperature of700˜800° C., and for 20˜40 seconds.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate an embodiment of the invention,and, together with the description, serve to explain the principles ofthe invention.

FIGS. 1A to 1B are partial sectional views used to describe aconventional method for manufacturing a MOS transistor.

FIGS. 2A to 2E are partial sectional views used to describe a method formanufacturing a MOS transistor according to an embodiment of the presentinvention.

DETAILED DESCRIPTION

Embodiments of the present invention will now be described in detailwith reference to the accompanying drawings.

FIGS. 2A to 2E are partial sectional views used to describe a method formanufacturing a MOS (metal-oxide-semiconductor) transistor according toan embodiment of the present invention.

With reference first to FIG. 2A, a field oxidation film 22 is formed ona predetermined region of a silicon wafer 21 using a LOCOS (localoxidation of silicon) or a trench process. The predetermined region ofthe silicon wafer 21 where the field oxidation film 22 is formed isreferred to as a device separation region, while all other areas arereferred to as a device region. A gate oxidation film 23 is grown on asurface of the silicon wafer 21 in the device region by performingthermal oxidation of the silicon wafer 21.

Next, polysilicon is deposited over an entire surface of the siliconwafer 21 on a side of the same on which the gate oxidation film 23 isgrown, thereby forming a gate electrode 24. Using the gate electrode 24as a mask, a p-type or n-type dopant is ion-injected in the deviceregion of the silicon wafer 21 such that LDDs (lightly doped drains) 25are formed on the silicon wafer 21, and side walls 26 are formed to bothsides of the gate oxidation film 23 and the gate electrode 24. Followingthis procedure, a conducting dopant identical to that used for the LDDs25 is ion-injected at a high concentration on the device region of thesilicon wafer 21 using the side walls 26 and the gate electrode 24 as amask to thereby form a source 27 and a drain 27.

Subsequently, using a sputtering method, titanium 28 is deposited to athickness of approximately 300˜500 Å over the entire surface of thesilicon wafer 1 on which the source 27 and drain 27 are formed, then anisolation oxidation film 29 is formed over the titanium 28 using PECVD(plasma enhanced chemical vapor deposition) to a thickness of roughly800˜1200 Å. Preferably, the titanium is deposited to a thickness of 400Å and the isolation oxidation film 29 is deposited to a thickness of1000 Å. Cobalt may be used in place of the titanium 28.

Following the above processes, a photosensitive film is deposited on theisolation oxidation film 29, then this film is exposed and developed tothereby form a counter active pattern 30 that exposes only the deviceregion. The counter active pattern 30 is then used as a mask to performwet etching of the isolation oxidation film 29 and remove the same.Therefore, the isolation oxidation film 29 is left remaining only overthe field oxidation film 22 as shown in FIG. 2B.

Next, RTP (rapid thermal processing) is performed for about 20˜40seconds at a temperature of roughly 700˜800° C. while injecting nitrogenat a flow rate of approximately 50 sccm. As a result, titanium silicide28′ is formed by the reaction between the titanium 28 and silicon. Thepreferable temperature and time of performing RTP for the formation ofthe titanium silicide 28′ are 750° C. and 30 seconds, respectively. Thetitanium 28 covering the side walls 26 and the field oxidation film 22is unable to be reacted with the silicon and so remains as unreactedtitanium 28.

Following the above, the unreacted titanium 28 is removed. In thisregard, since the unreacted titanium 28 that covers the field oxidationfilm 22 is itself covered by the isolation oxidation film 29, only theunreacted titanium 28 that covers the side walls 26 is extracted in thisremoval process as shown in FIG. 2C. The isolation oxidation layer 29left remaining over the field oxidation film 22 is then removed using asolvent.

Subsequently, RTP is performed for about 20˜40 seconds at a temperatureof roughly 700˜800° C. while injecting oxygen at a flow rate ofapproximately 50 sccm. Hence, the unreacted titanium 28 over the fieldoxidation film 22 is oxidized and formed into a titanium oxidation film31 as shown in FIG. 2D. The preferable temperature and time ofperforming RTP for the formation of the titanium oxidation film 31 are750° C. and 30 seconds, respectively. In this process, the titaniumsilicide 28′ in the device region undergoes almost no reaction with theoxygen. Next, in order to reduce the resistance of the titanium silicide28′ and increase the strength of the same, a heat process is performedin a nitrogen environment, at a temperature of approximately 850˜950°C., and for 5˜15 seconds, preferably at a temperature of 910° C. and for10 seconds.

Following the above, in order to form a film for use as an etchingcompletion layer during etching to form contact, a silicon nitride film32 is formed to a thickness of roughly 200˜400 Å using PECVD. Thesilicon nitride film 32 is preferably formed to a thickness of 300 Å.

Next, an insulating layer, that is, a PMD (pre-metal dielectric) layer33 is thickly formed on the silicon nitride film 32 using APCVD(atmospheric pressure chemical vapor deposition), after which the PMDlayer 33 is heat treated at a temperature of 600˜800° C. for 30˜50seconds such that the strength of the PMD layer 33 is increased. CMP(chemical mechanical polishing) is then performed to flatten the PMDlayer 33. Heat treating of the PMD layer 33 is preferably performed at atemperature of 700° C. and for 40 seconds.

Subsequently, to prepare for the formation of contact holes, aphotosensitive film pattern 34 is formed on the flattened PMD layer 33.Next, with reference to FIG. 2 e, exposed areas of the PMD layer 33 areetched using the photosensitive film pattern 34 as a mask to therebyform contact holes 35. Since the titanium oxide film 31 is formed on thefield oxide film 22, excessive etching of the field oxide film 22 wherethe field oxide film 22 is depressed adjacent to the device region isavoided.

TiN 36 is then thinly deposited as a barrier metal film over the entiresurface of the silicon wafer 21 on which the above elements are formed,after which tungsten 37 is used to cover all elements and fill thecontact holes 35.

Further, a metal thin film (not shown) is deposited and patterned on thePMD layer 33 such that a metal wiring layer (also not shown) thatconnects to tungsten plugs filling the contact holes 35 is formed. Thiscompletes the semiconductor device.

In the method for manufacturing a MOS transistor according to theembodiment of the present invention described above, the isolationoxidation film is used so that unreacted titanium is left remaining onthe field oxidation film, and the remaining unreacted titanium isoxidized to form the titanium oxidation film. As a result, the presentinvention prevents contact spiking in which there occurs excessiveetching (into even the field oxidation layer adjacent to the deviceregion) caused by the formation of depressions in the field oxidationfilm itself during the process of etching to form the contact holes ormis-alignment of the photosensitive film pattern. Therefore, currentleakage and mis-operation of the device caused by contact spiking areprevented.

Although embodiments of the present invention have been described indetail hereinabove, it should be clearly understood that many variationsand/or modifications of the basic inventive concepts herein taught whichmay appear to those skilled in the present art will still fall withinthe spirit and scope of the present invention, as defined in theappended claims.

1. A method for manufacturing a metal-oxide-semiconductor transistor,comprising: forming a metal thin film and an isolation oxidation film ona semiconductor substrate, and selectively etching the isolationoxidation film such that the isolation oxidation film is left remainingonly over a field oxidation film; heat treating the semiconductorsubstrate to form suicide by the metal thin film in gate, source, anddrain regions; removing portions of the metal thin film that is notformed into silicide; removing the isolation oxidation film leftremaining on the field oxidation film; and heat treating thesemiconductor substrate in an oxygen environment to form the unreactedmetal thin film remaining on the field oxidation film into a metaloxidation film.
 2. The method of claim 1, wherein the metal thin film isformed by depositing a metal such as titanium and cobalt to a thicknessof about 300 to 500 Å.
 3. The method of claim 1, wherein the silicide isformed by performing rapid thermal processing of the metal thin film ina nitrogen environment, at a temperature of about 700 to 800° C., andfor about 20 to 40 seconds.
 4. The method of claim 1, wherein followingthe formation of the metal oxidation film, rapid thermal processing isperformed in a nitrogen environment, at a temperature of about 850 to950° C., and for about 5 to 15 seconds.
 5. The method of claim 1,wherein the isolation oxidation film is formed by performing depositionto a thickness of about 800 to 1200Å using plasma enhanced chemicalvapor deposition.
 6. The method of claim 1, wherein the metal oxidationfilm is formed by performing rapid thermal processing in an oxygenenvironment, at a temperature of about 700 to 800° C., and for about 20to 40 seconds.